Also known as: Blacklist, DNSBL, RBL
A published list of IP addresses or domains known for sending spam, used by mail servers to block or filter senders.
An email blocklist (historically "blacklist," technically a DNSBL or RBL) is a database of IPs or domains associated with spam and abuse. Mail servers query these lists in real time; if your sending IP or domain appears, your mail may be rejected or filtered before it is ever seen. Spamhaus is the best-known operator.
You land on a blocklist by behaving like a spammer — high bounce rates, spam-trap hits, sharp volume spikes, or many complaints. Shared IPs can also tar you with a neighbour's behaviour.
Getting delisted means fixing the underlying cause and requesting removal. As with most deliverability problems, prevention via clean lists and verification is far cheaper than recovery.
An email address used by mailbox providers and blocklists to identify senders with poor list hygiene.
A trust score that mailbox providers assign to your sending IP and domain, which determines whether your mail reaches the inbox.
The percentage of sent emails that could not be delivered and were returned by the receiving server.
See it in action
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